Bill, are you refering to James and Ann Harlan, Robert Lincoln's in-laws? Robert married their daughter Mary Eunice Harlan in September,1868.
Robert and Mary did name their 1st child (who was born in October,1869) after Robert's mother Mary.
Excuse me, I should have been more specific. The couple I am thinking of had their daughter while Abraham Lincoln was still alive.
So when is this "Old Enough To Know Better" supposed to kick in?